This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-029907, filed Feb. 6, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a solid-state imaging device of flat panel detection type in which photoelectric conversion pixels are arrayed in the shape of a matrix, and which is applied to, for example, an X-ray diagnosis apparatus for medical treatment.
2. Description of the Related Art
In recent years, in the field of medical treatment, the medical data of patients have been databased for the purpose of performing therapies promptly and accurately. Databasing has been required also for the image data of X-ray radiography, and the digitization of X-ray radiographic images has been desired. Since, however, the images are radiographed with a silver halide film in a conventional X-ray diagnosis apparatus for medical treatment, the digitization thereof needs to be implemented in such a way that, after the radiographed film has been developed, it is further scanned by a scanner or the like so as to convert the images into electric signals, followed by a digital process. Accordingly, labor and time are expended on the digitization of the images. Therefore, a system wherein the images are directly digitized using a CCD (charge coupled device) imager of one inch square or so has recently been put into practical use.
In this regard, in a case where the lungs of a subject, for example, are to be radiographed, an area necessary for the radiography is as large as about 43 cmxc3x9743 cm. Therefore, an optical apparatus for condensing the light of the whole area onto the CCD imager is necessitated, and the inevitable large size of the apparatus becomes a problem. A solid-state imaging device of flat panel detection type has been proposed as means for solving the problem. As an example of the device, an X-ray imaging device called xe2x80x9cflat panel X-ray detectorxe2x80x9d is proposed in U.S. Pat. No. 4,689,487.
The above solid-state imaging device of flat panel detection type is characterized by employing a-SiTFTs (amorphous silicon thin-film transistors) as the control elements of photoelectric conversion pixels. Now, the structure of this device will be briefly explained.
A flat substrate made of a glass material is employed for the device. An insulating layer made of a silicon oxide film is formed on the substrate, and photoelectric conversion pixels each consisting of a capacitor, a TFT and an X-ray/charge conversion film are formed in the shape of a matrix on the insulating layer. Further, there are formed the wiring patterns of scanning lines for feeding switching control signals to the TFTs of the respective pixels arrayed in the row direction of the matrix, and the wiring patterns of signal lines for sequentially transferring stored charges read out from the respective pixels arrayed in the column direction. The substrate is called xe2x80x9cTFT array substratexe2x80x9d.
With the device of the above construction, in each of the pixels, a bias voltage is applied to a capacitor forming portion through a capacitor line beforehand, and charges generated by the X-ray/charge conversion film are stored in the capacitor. The TFTs of the respective pixels are sequentially driven to turn ON through the scanning lines laid in row units, whereby the stored charges of the pixel capacitors are sequentially derived to the signal lines laid in column units. The stored charges of the individual pixels derived to the respective signal lines are amplified, and are digitally outputted. Thus, image data based on all the pixels can be obtained.
In the TFT array substrate, terminals for connections with circuit devices such as drive circuits, an amplification circuit and a power source circuit, which are prepared separately from the substrate itself, are formed at the respective terminating ends of the scanning lines, signal lines and capacitor lines. The terminals are put together by every predetermined number (each terminal shall be called a xe2x80x9cPADxe2x80x9d, and the group of the terminals put together (the collection of PADs) shall be called a xe2x80x9cPAD groupxe2x80x9d). By way of example, the terminals are arranged at a high density under the conditions of a terminal width of 60 xcexcm and a terminal pitch of 100 xcexcm.
A technique called xe2x80x9cTAB (Tape Automated Bonding) connectionxe2x80x9d is employed for connecting the terminals and the circuit devices. The TAB connection implements the electrical connections among the terminals arranged at the high density, in such a way that a PAD region on the TFT array substrate and a PAD region on the side of a flexible circuit board, which is called a tape carrier package (TCP) and on which the circuit devices are mounted (hereinbelow, the circuit board shall be termed the xe2x80x9cTCPxe2x80x9d), are bonded by thermocompression bonding through an anisotropic conductive film (ACF) of thermosetting type.
Since the TFT array substrate is very expensive, it needs to be repaired at the time when any misconnection with the TCP has occurred. A repairing method in this case is such that the TCP thermally secured is torn off from the TFT array substrate, that the ACF secured on the surface of the substrate is removed with a solvent or the like, and that the substrate and the TCP which have been properly connected are bonded again by the thermocompression bonding through an ACF. In the prior art, therefore, the whole wiring patterns which include terminal forming portions are formed of a material which is difficult to peel off the substrate at the tearing-off of the TCP or at the removal of the ACF, for example, molybdenum-tungsten (MoW) which is used for the capacitor lines. Besides, a transparent conductive film of indium tin oxide (ITO) or the like is stacked as a protective layer on the terminal forming portions.
Meanwhile, an image of high definition and the reduction of image noise are required of the above solid-state imaging device of the flat panel detection type. For meeting the requirements, it is indispensable to lower the resistance of each signal line forming a factor for the image noise, and to reduce a capacitance parasitic to the signal line. It is desirable for the decrease of the parasitic capacitance of the signal line to fine the line width of each scanning line which intersects orthogonally to the signal line, and the use of a material of low resistance is mentioned as means for fining the scanning line with a predetermined driving speed satisfied. For attaining the lower resistances of the scanning line and the signal line, it is desirable to use, for example, an aluminum alloy.
The material such as aluminum alloy, however, weakly couples with the silicon oxide film. The terminals for the TAB connection are formed at the terminating ends of the wiring patterns which form the scanning lines and the signal lines. Therefore, in a case where the aluminum alloy is used as the material of the wiring patterns, even the wiring layers are peeled off at the removal of the ACF. For this reason, a new terminal structure of the TFT array substrate is demanded in points of facilitating the repair and improving the characteristics of the imaging device.
Incidentally, a technique which employs an aluminum alloy as a wiring material for elements arrayed in the shape of a matrix is proposed in Japanese Patent Laid-Open No. 2000-243558. The technique disclosed in the cited reference is as stated below.
With the object of raising a scanning drive speed simultaneously with heightening an integration density, the wiring patterns of scanning lines and signal lines for light emitting display elements are formed of the aluminum alloy. The terminating ends of the wiring patterns are shaped into terminals for connections with external circuit devices. The whole substrate except terminal portions are tightly sealed. On this occasion, when the aluminum alloy is exposed the terminal portion is corroded by oxidation. Therefore, the terminal portions are covered with protective films made of a material such as molybdenum.
The technique disclosed in the cited reference relates to a light emitting display, and differs in the technical field from the flat panel type solid-state imaging device of the present invention. Further, it does not implicate at all the demand for facilitating the repair treatment of the substrate. Granted that the substrate is submitted to the TAB connection at the terminal portions indicated in the cited reference, even wiring layers will be peeled off at the removal of an ACF because the terminal portions are made of the aluminum alloy. It is therefore obvious that the object of the present invention to simultaneously satisfy the facility of the repair and the improvements of the characteristics cannot be accomplished by the technique in the cited reference.
As explained above, in the prior-art solid-state imaging device of flat panel detection type, especially image noise is a serious problem, and the reduction of the image noise is eagerly requested. Lowering the resistances of wiring patterns is therefore desired, but the use of a material of low resistance is difficult on account of the restriction of a terminal structure.
An object of the present invention is to provide a flat panel detection type solid-state imaging device including a terminal structure which permits the imaging device to be easily repaired with respect to external circuit devices while realizing the enhancement of an operating speed and the reduction of image noise based on the lowered resistances of wiring patterns.
According to a first aspect of the present invention, there is provided a flat panel detection type solid-state imaging device, comprising a flat substrate; an array structure which is formed on the flat substrate, and which includes a plurality of conversion pixels for converting incident light or an incident radiation into charges and then storing the charges, a first group of wiring patterns for feeding control signals to the conversion pixels, and a second group of wiring patterns for transferring charges read out from the conversion pixels; and terminal structures which are formed on the flat substrate, and each of which includes a terminal pattern for TAB (Tape Automated Bonding) connection which is connected with a terminating end of any of the wiring patterns of the first and second groups of wiring patterns; wherein a first material which couples more intensely than a second material of the wiring patterns in respect of the TAB connection is employed for the terminal patterns, and the second material of the wiring patterns has a resistance lower than that of the first material.
According to a second aspect of the present invention, there is provided a flat panel detection type solid-state imaging device, comprising a flat substrate; an array structure which is formed on the flat substrate, and which includes a plurality of conversion pixels for converting incident light or an incident radiation into charges and then storing the charges, a first group of wiring patterns for feeding control signals to the conversion pixels, and a second group of wiring patterns for transferring charges read out from the conversion pixels; and terminal structures which are formed on the flat substrate, and each of which includes a terminal pattern for TAB (Tape Automated Bonding) connection as is formed at a position near a terminating end of any of the wiring patterns of the first and second groups of wiring patterns; and connection structures which are formed on the flat substrate, and each of which includes a conductive pattern that is stacked on an end part of the terminal pattern and the terminating end of the wiring pattern so as to overlap them partially, and that serves to electrically connect both the terminal pattern and the wiring portion; wherein a first material which couples more intensely than a second material of the wiring patterns in respect of the TAB connection is employed for the terminal patterns, and the second material of the wiring patterns has a resistance lower than that of the first material.
In accordance with the present invention, lower resistances can be realized by optimizing the selection of the material(s) of signal lines or/and scanning lines, whereby the noise of an imaging device is reduced, and the driving speed thereof is enhanced. Besides, a terminal construction can be made equivalent to that of the prior art, so that the repair facility of the imaging device is excellent.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.